Maintaining sobriety takes a WHOLE lot more than just going to meetings. Its great that he has been clean all this time but being clean in a Rehab center is a lot different than being clean on the outside. In Rehab we addicts are all in a cocoon, protected from any dangers, triggers, temptations, etc, so it is very easy to stay clean. Once we get out of Rehab is when the real recovery process begins.
One thing to remember, when I was first trying to get clean my ex was doing much of the same that you are doing right now with your bf. Moved in with her, she tried to help me re-focus my life away from dealing // using. The whole 9 yards. I just want you to keep in mind something, if he does slip up and starts using again don't take it that he doesn't love you or as a slap in the face because that is simply not the case. So many times I let my ex down but it was not on purpose like she suggested. The dope just had to strong a pull to me.
Its good that your optimistic that will help the both of you in the long run. Best of luck to the both of you, keep us updated.